Microfluidic systems, that is, systems or devices having channels or chambers that are fabricated on the micron or submicron scale, are used to perform a multitude of chemical and physical processes on a micro-scale. Individual components of the microfluidic systems can be used alone or together, for example, to control or measure the transport of fluid inside microchannels. Typical applications for microfluidic systems include analytical and medical instrumentation, industrial process control equipment, and liquid and gas phase chromatography. In these systems, methods to reliably aliquot volumes of sample from one conduit into a second conduit are important for performance of the analysis. In some cases, sample volumes as small as 1 nL are required for analysis, which is a volume too small to be reliably dispensed by known macroscale methods, such as conventional valves or pipettes. It would be advantageous to have a microfluidic system that could be used with a wide range of processes and process liquids and could be fabricated on a microchip platform. It would also be advantageous to have a device with a fast response time and precise control over small sample volumes and flows.
Microfluidic control devices, such as microvalves manufactured from silicon or elastomers, including devices fabricated from hydrogels, soft elastomers with control lines embossed in a substrate, and devices fabricated with structures that are free to move within microchannels are currently known. More information on these devices can be found in Shoji and Esashi, J., Micromech. Microeng., 4, 157-171, 1994; Beebe et al., Nature, 404, 588-590, April, 2000; Unger et al., Science, 288, 113-116, April, 2000; and Rehm et al., uTAS 2001, 227-229, October, 2001. Disadvantageously, however, these devices suffer from one or more of the disadvantages of not being easily integrated into microchip platforms, have excess dead volume, high power requirements, slow response times, are difficult and costly to manufacture and assemble, are able to withstand only modest pressure differentials, are restricted to a narrow range of processes and process liquids, are subject to solvent-induced deformation effects, exhibit performance variations from minor variations in material properties, and respond poorly to solvent-induced shrinkage and swelling.
Therefore, there is a need for a microfluidic control device that has a fast response time, precise control over small gas and liquid flows, and precise control over small gas and liquid volumes in the channels and chambers of microfluidic systems. There is also a need for a microfluidic control device that can be integrated into a microchip platform and is compatible with a wide range of chemical solvents that are used in microfluidic systems.